Samples Preparation Method

Sample preparation requirements vary depending on sample type and requested analysis. Proper drying, homogenization, storage, and labeling are required to ensure accurate analytical results.

Select the preparation procedure below for soil, organic carbon, plant tissue, or liquid sample analyses. Contact SASC if sample preparation requirements are unclear before submission.

Sample Preparation Procedures

Preparing soil samples for total carbon and nitrogen analysis using an Elemental Analyzer:

1. Dry 20 g of the homogenized soil sample at 55°C for one week.
2. Pass dried soil through a 2 mm sieve.
3. Place the dried and sieved sample in a large coin envelope labeled in pencil with the researcher's initials and sample ID.
4. Grind the soil samples in a ball mill grinder for 1 to 3 minutes.
5. Put ground soil samples in a coin envelope and dry for >1 day at 55°C
6. Transfer dried samples to the CN sample desiccator.
7. Weigh approximately 50-60 mg of soil into tin capsules using a microbalance. Record the weight to three decimal places (i.e., 0.000 mg). For soil with higher organic carbon content, weigh 20-30 mg. 
8. Fold the tin capsule to eliminate air in the sample, forming a square so the sample does not roll, and place it in a well plate.
9. Enter weights and sample IDs into the spreadsheet.

Preparing soil samples for organic carbon analysis using an Elemental Analyzer:

1. Dry 20 grams of homogenized soil at 55°C for one week.
2. Pass the dried soil through a 2 mm sieve.
3. Place the dried and sieved soil in a coin envelope labeled in pencil with the researcher's initials and sample ID.
4. Grind the soil using a ball mill grinder for 1 to 3 minutes.
5. Put the ground soil into the coin envelope and re-dry for over a week at 55°C.
6. Transfer the dried samples to a desiccator to store them in a dry environment until ready for weighing and further processing.
7. Using a microbalance, weigh approximately 30-40 mg of soil into silver capsules. Record the weight to three decimal places (i.e., 0.000mg), leave the capsule open, and place it in a well plate.
8. Add 0.2-0.3 ml of 1:1 12M HCl to the silver capsule.
9. Move the well plate to an oven and dry it at 65°C for 2 weeks.
10. Fold and seal the silver capsule tightly. Before folding, consider placing a tin capsule around the silver one to prevent breakage, and place it in a well plate.

Note: To measure inorganic carbon, a separate sample must be analyzed for total carbon to determine the inorganic carbon content.

Plant tissue processing procedures

1. Dry plant material at 55°C for one week.
2. Homogenize and grind a large amount of plant material (more than a handful) using a Wiley mill, and subsample if necessary. If an adequate sample is not available, use a mortar and pestle.
3. Dry ground and homogenize plant samples in labeled coin envelopes at 55°C
4. Store dried samples in a desiccator
5. Weigh ~ 5-10 mg of plant material into tin capsules using a microbalance. Record the weight to three decimal places (i.e., 0.000mg), and place it in a well plate.
6. Enter weights and sample IDs into the spreadsheet.

Liquid Sample Preparation Procedures

Submit liquid and extracted samples in clean, labeled containers with sample IDs and requested analytes clearly identified.

For nutrient analysis using the OI Analytical Flow Solution system (ammonium-N, nitrate/nitrite-N, nitrite-N, and orthophosphate-P), indicate the sample matrix on the submission form.

For extracted soil nutrient samples (OI Analytical):

1. Ammonium nitrogen (NH4-N), nitrate/nitrite nitrogen (NO3/NO2-N), and nitrite nitrogen (NO2-N) are typically extracted using 2 N KCl. The minimum volume of the extracted sample should be 20 mL. After the extraction process, the samples must be filtered using a 0.4 µm filter. Following filtration, the samples should be immediately frozen and kept frozen until they are submitted for analysis.
2. Orthophosphate-P (PO4-P) extraction methods vary depending on soil type and project requirements; therefore, the extraction matrix must be specified at submission.

For TOC/TN analysis (TOC-L):

Please submit samples in clean containers. Clearly indicate whether analyses for total organic carbon (TOC), total nitrogen (TN), or both are required. Include information about the extraction method, sample matrix, filtration details, dilution factors, storage conditions, and any preservation requirements, if applicable. The minimum volume for the extracted sample should be 45 mL.